In a CRT display, it is necessary to produce a parabolic signal for use in the display's horizontal focus circuitry. As display scanning frequencies increase and screen sizes increase, it becomes particularly important for the parabolic signal to be free of spuriae and other harmful effects in order to produce sharp scanning lines in the raster and small details in the displayed picture.
In a known integrated circuit device for driving a CRT display, a parabolic waveform is generated by use of a circuit using a ramp generator, a parabola generator (typically a squaring circuit), a buffering circuit and a blanking circuit. The use of this large number of circuits increases the IC's size and design complexity and impacts its quality of operation.
Also, in this known integrated circuit device the parabolic waveform is produced having a fixed delay relative to a horizontal flyback pulse. This fixed delay requires the use of accompanying external circuitry which has a complementary delay so that the total delay from both the integrated circuit and the external circuitry is equal to one period of the horizontal flyback signal.
It is an object of this invention to provide a parabolic signal generator for use in a cathode ray tube (CRT) display circuit in which one or more of the above disadvantages may be overcome or at least alleviated.